Cephalization - Research Article from Macmillan Science Library: Animal Sciences

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Cephalization in the Animal Kingdom

Even hydras, which are primitive, radially symmetrical cnidarians, show some degree of cephalization. They have a "head" where their mouth, photoreceptive cells, and a concentration of neural cells are located.

Flatworms (phylum Platyhelminthes) are the most primitive animals with bilateral symmetry. They also have a fairly advanced degree of cephalization, with sense organs (photosensory and chemosensory cells) and a brain concentrated at the anterior end. Consequently, scientists believe that cephalization characterized all bilaterally symmetrical animals from their origins. However, flatworms differ from more advanced animals in that their mouths are in the center of their bodies, not at the anterior end.

In arthropods, cephalization progressed with the incorporation of more and more trunk segments into the head region. Scientists believe this was advantageous because it allowed for the evolution of more effective mouth-parts for capturing and processing food.

Cephalization in vertebrates, the group that...

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This section contains 1,013 words
(approx. 4 pages at 300 words per page)
Buy the Cephalization Encyclopedia Article
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Macmillan Science Library: Animal Sciences
Cephalization from Macmillan Science Library: Animal Sciences. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.
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